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You can select a single field in MongoDB using the following syntax: db. yourCollectionName. find({"yourFieldName":yourValue},{"yourSingleFieldName":1,_id:0});
In MongoDB, we can check the existence of the field in the specified collection using the $exists operator. When the value of $exists operator is set to true, then this operator matches the document that contains the specified field(including the documents where the value of that field is null).
Yeah, it's possible using $exists:
db.things.find( { a : { $exists : false } } ); // return if a is missing
When is true, $exists matches the documents that contain the field, including documents where the field value is null. If is false, the query returns only the documents that do not contain the field.
If you don't care if the field is missing or null (or if it's never null) then you can use the slightly shorter and safer:
db.things.find( { a : null } ); // return if a is missing or null
It's safer because $exists will return true even if the field is null, which often is not the desired result and can lead to an NPE.
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